1. Technical Field
The present invention relates to an electronic balance, and in particular, an electronic balance which can measure an object by selecting an appropriate measurement mode (display conditions) in accordance with the state of the object to be measured, the task of measurement and the environment for the task.
2. Background Technology
In general electronic balances, the measured weight, which is gained by detecting the weight of an object, is in many cases affected by vibration when the object is placed on the measuring dish, or vibration from the outside caused by the surrounding environment, such as air flow or vibration in the floor. In the case where an object is measured under the influence of an air flow blown out from an air conditioner, for example, the balance shakes, due to the air flow from the air conditioner, and therefore, the measured weight keeps fluctuating over the duration of measurement.
Therefore, electronic balances having a windproof structure for preventing the electronic balance from being affected by air flow are disclosed (see for example Patent Document 1).
Meanwhile, electronic balances where fluctuation in the measured weight of an object is negated through an averaging process are also used. That is to say, electronic balances having an averaging function for repeatedly detecting the weight of the object and storing the measured weight in a buffer in sequence so that the measured weight, of which the number of samples is preset, from among the measured weight stored in the buffer, are averaged, and thus, the average weight is calculated and displayed on a display screen, have been developed.
In electronic balances having an averaging function, it is necessary to remove the weight measured in a vibrating state immediately after the object is placed on and removed from the measuring dish from the sampling data for the averaging process. Therefore, the threshold value of the fluctuation width of the measured weight for determining whether or not the object is in a vibrating state (hereinafter referred to as amount of fluctuation in weight for starting averaging) and the threshold value of the time during which the state where the fluctuation width of the measured weight is the amount of fluctuation in weight for starting averaging or lower (hereinafter referred to as stability continuing time) are set so that it can be determined whether or not the object is in a vibrating state from the relationship between the measured weight detected in sequence and the above described threshold values.
That is to say, when the amount of fluctuation in the weight which indicates chronographic change in the measured weight detected in sequence (weight fluctuation width) is determined to be the amount of fluctuation in weight for starting averaging or lower, and the time during which the state continues after the amount of fluctuation in the weight becomes the amount of fluctuation in weight for starting averaging or lower is determined to be longer than the stability continuing time or greater, and thus, it is determined that the object is in a “stable state,” and in such a state that the averaging process is possible.
When the object is determined to be in a “stable state,” the measured weight starts being used, and when a preset number of samples are gained for the measured weight, the average weight is calculated, and this calculated average weight is displayed on the display screen as the results of measurement of the “weight” of the object.
As described above, in the case where various types of vibration noise are included in the measured weight, the average weight is gained after the effects of the noise have subsided and the object becomes of a “stable state.”
Incidentally, electronic balances having an averaging function use the measured weight of a preset number of samples in to calculate the average weight, and therefore, in the case where the preset number of samples is great, time is required before the average weight can be displayed on the display screen, and as a result, it takes time for the measurer to gain the average weight of the object. In contrast, in the case where the preset number of samples is small, the effects of averaging become small, and it becomes difficult to gain a stable average weight.
In addition, in the case where a desired amount is taken by adding (or removing) the object (for example powder or liquid) little by little, the value gained through the averaging process on the measured weight before and after a small amount is added or removed is displayed, unless the measured weight before and after the operation of adding or removing a small amount is removed from the averaging process. However, in the case where the amount of fluctuation in the weight becomes small as a result of the object being added or removed, the amount of fluctuation in the weight becomes a preset amount of fluctuation in weight for starting averaging or less, and the state continues for the stability continuing time or longer, and thus, an average weight resulting from inappropriate sampling is displayed.
Accordingly, it is desired for the averaging process to be adjusted so that the averaging process becomes appropriate for the situation in accordance with whether the object is light or heavy, the task of measurement (simple measurement of weight, gradual measurement) and the environment for the task. Therefore, electronic balances having an averaging function where a “measuring mode” in which the averaging process can be adjusted so that it is appropriate in accordance with the object, the measurement task and the environment for the task can be selected have been developed.
For example, a “standard measuring mode” is provided for an averaging process which is appropriate for general measurement, and a “gradual measuring mode” is provided for measuring a desired amount of an object by adding (or removing) a small amount of the object in sequence. For cases where it is necessary to carry out measurement in an environment where there is a lot of vibration from the outside, such as vibration in the floor, a “disturbance-proof mode” is additionally provided. Measuring modes other than these may be added.
In addition, such parameters as the number of samples required to be set when the averaging process is carried out, the amount of fluctuation in weight for starting averaging and the stability continuing time are provided with appropriate values for each measuring mode as “averaging parameters,” and when the measuring mode is selected, the averaging process is carried out with the number of samples and the amount of fluctuation in weight for starting averaging and the stability continuing time.
As a result, when the number of samples set in standard measuring mode is used as a reference, selection of a measuring mode where a smaller number of samples is set makes the time for calculating the average weight shorter than the standard measuring mode, that is to say, makes the response of the average weight displayed faster, and therefore, the object can be placed on the measuring dish and removed quickly. In addition, when the amount of fluctuation in weight for starting averaging set in standard measuring mode is used as a reference, and a measuring mode where a smaller amount of fluctuation in weight for starting averaging is set is selected, the amount of fluctuation in the weight when the object is added or removed tends to be greater than the amount of fluctuation in weight for starting averaging in the case where a small amount of the object (for example powder or liquid) is added (or removed) in sequence, and thus, it can become difficult to start the averaging process during the process of adding or removing the object.
In the following, in order to make the description more simple, an electronic balance having an averaging function where two measuring modes: a “standard measuring mode” and a “gradual measuring mode,” where the preset number of samples is different can be selected is described.
In an electronic balance having an averaging function as that described above, the average weight calculated through an averaging process is displayed on a display screen as the results of measurement of the “weight” of the object. At this time, it is required for the electronic balance to be in a “stable state,” and at the same time, it is required for the response in gaining the results of measurement to be fast.
Here, “stability of the average weight” and “response of the average weight” in the electronic balance in a “stable state” are described.
The “stability of the average weight” improves as the set number of samples for calculating the average weight increases. However, when the number of samples is great, the time required before the average weight can be displayed on the display screen becomes long.
Meanwhile, in order to increase the “response of the average weight,” the number of samples for calculating the average weight should be set as small as possible. However, when the number of samples becomes too small, the average weight easily fluctuates, due to failure to subdue the effects of various types of vibration noise.
That is to say, the “stability of the average weight” and the “response of the average weight” are inversely related by nature.
Therefore, two measuring modes (display conditions): “standard measuring mode,” where the set number of samples is great, and “gradual measuring mode,” where the set number of samples is small, are stored in advance in conventional electronic balances, taking the balance between the “stability of the average weight” and the “response of the average weight” into consideration. As a result, the user of the electronic balance selects either the “stability of the average weight” or the “response of the average weight” in accordance with the application and the environment for use in each case, and thus, measures the object.
Patent Document 1: Japanese Unexamined Patent Publication H9 (1997)-43041